1. Field of the Invention
The invention relates to the field of microwave ovens and more particularly to combination microwave, convection and broiling ovens.
2. Brief Description of the Prior Art
The concept of a combination microwave/convection and broiling oven is known. See e.g., U.S. Pat. No. 3,716,687 filed Aug. 18, 1971 to R. J. W. Constable. Some prior ovens employ certain features of the present invention, such as including a quartz infrared lamp in the oven for the purpose of broiling, see e.g., U.S. Pat. Nos. 4,096,369 filed Nov. 15, 1976 to Tanaka et al. (assigned to Matsushita Electric Industrial Co., Ltd. of Japan) and 3,878,350 filed July 14, 1972 to Takagi (assigned to Sharp Kabushiki Kaisha of Japan), or a hot air convection means, see e.g., U.S. Pat. No. 4,262,183 filed Sept. 24, 1979 to Smith et al. (assigned to the General Electric Co.).
In the only known prior use of quartz infrared lamps in a microwave oven, the lamps are enclosed in a wire mesh to shield them from microwaves. See the above-referenced '369 and '350 patents. The resulting structures not only occupy valuable oven space, but are also not easily removable or cleanable. In addition, the wire mesh masks a good deal of the infrared, thereby restricting the efficiency of the lamp and unnecessarily heating the microwave shield up to a high temperature.
The quartz infrared lamp structure of the present invention not only has no in-cavity microwave shield, which leads to a much higher infrared efficiency, but the lamp is also removable both for easy cleaning and for providing a larger oven cavity for microwave-only operation.
The power leads to the quartz lamps act as antennae thus potentially conveying a large amount of microwave energy out of the cavity. To prevent the escape of microwaves along a heater's power leads, a quater-wave choke has conventionally been employed external to the oven cavity. See e.g., U.S. Pat. Nos. 4,298,780 filed Mar. 12, 1980 to Suzuki and 4,149,056 filed May 5, 1977 to Kaneshiro et al. (assigned to Sharp Kabushiki Kaisha of Japan). It is a common feature of these chokes that they are not designed to be operable with the infrared heating element removed. In contrast, the choke design of the present invention allows removal of the infrared heaters during microwave operation. When removed, they may be easily cleaned.
Constable '687 and Smith et al. '183 both prefer to heat air for convection by blowing it across shielded-rod heaters. This practice appears to be conventional. The heaters themselves are not employed as a source of direct infrared radiation for broiling. Further, the air blowing across them restricts the high temperature that is normally associated with broiling.
In contrast, the present invention uses the quartz infrared lamp both for broiling and for convection heating.
The convection fans of the prior ovens do not perform the additional function of heat exchanging. The present invention's convection fan comprises a rotating heat exchanger/fan which absorbs heat from the quartz lamp, transmits it to the air and blows it down the sides of the cavity. The heat exchanger/fan of the present invention has the additional advantages of broadcasting reflected high-frequency infrared about the cavity, and, as it itself heats up, it creates a broad source of low-frequency infrared radiation.